1. Field of the Invention
The present invention relates to a scanning exposure apparatus and a device manufacturing method of manufacturing a device using the same.
2. Description of the Related Art
Lithography is well known as a method of forming a circuit pattern on a wafer. In lithography, a circuit pattern formed on a reticle is projected onto a wafer, thereby exposing the wafer. The wafer is coated with a photosensitive agent, on which a latent image is formed by exposing the wafer. This latent image is visualized into a physical pattern by a developing process.
In the wafer process of the semiconductor device manufacturing process, a circuit pattern is formed by repeating a step of oxidizing the wafer surface, a step of forming an insulating film, a step of forming an electrode by vapor deposition, an ion implantation step, and an etching step. In this wafer process, the thickness of the insulating film or that of the photosensitive agent in an exposure process often becomes nonuniform. When a wafer on which an insulating film or photosensitive agent having a nonuniform thickness is formed as in this case is exposed, a shift in pattern line width or a failure in resolution is likely to occur, resulting in a decrease in the product yield. Especially in a step and scan exposure apparatus which generally has a relatively wide shot region, large nonuniformity in thickness is likely to occur in the shot region, resulting in a non-negligible failure in resolution.
Japanese Patent Laid-Open No. 7-29810 discloses a solution to the problem by changing the exposure light quantity of the exposure beam on the substrate in accordance with the position on the substrate by changing the illuminance, the time interval of pulse emission by a pulse emission light source, and the scanning speed of a stage.
FIG. 1 is a view illustrating the intensity of exposure light which strikes a wafer. In scanning exposure, the wafer is exposed by repeating light emission by the light source while moving the wafer stage in the direction of the scanning axis.
The barycentric position of the exposure light is the barycentric position of the light intensity distribution in the direction of the scanning axis, as shown in FIG. 1, and is calculated for each image height (each position in the direction of the slit axis). In this specification, a curve obtained by virtually connecting the barycentric positions at respective image heights is called a barycentric line.
When the exposure light quantity is changed in accordance with the method described in Japanese Patent Laid-Open No. 7-29810, a change in the exposure light quantity after scanning exposure (the time integral of the exposure light intensity) depends on the curvature of the barycentric line, as illustrated in FIGS. 2A and 2B. In the example shown in FIGS. 2A and 2B, the exposure light intensity linearly increases in the direction of the scanning axis.
FIG. 2A shows an example in which the barycentric line of the exposure light is parallel to the slit axis. FIG. 2B shows an example in which the barycentric line of the exposure light is curved. Referring to FIGS. 2A and 2B, the exposure light quantity in the scanning-exposed shot region exhibits nonuniformity that depends on the curvature of the barycentric line of the exposure light. In view of this, the barycentric line of the exposure light must be adjusted in accordance with the exposure light profile in changing the exposure light intensity in accordance with the position in the direction of the scanning axis. Note that the preferable shape of this barycentric line can be a straight line or a controlled curve according to the circumstances involved.